U.S. patent number 4,803,131 [Application Number 07/110,317] was granted by the patent office on 1989-02-07 for magnetic recording medium.
Invention is credited to Hiroaki Araki, Kiyomi Ejiri, Chiaki Mizuno, Hiroshi Ogawa, Shinji Saito.
United States Patent |
4,803,131 |
Saito , et al. |
February 7, 1989 |
Magnetic recording medium
Abstract
An improvement of a magnetic recording medium comprising a
nonmagnetic support and a magnetic recording layer provided on the
support which comprises a binder and a ferromagnetic powder
dispersed therein is disclosed. The binder contains a resin
component having an epoxy group and the ferromagnetic powder
contains water in an amount corresponding to moles of 1-5 times as
much as the number of moles of the epoxy group contained in the
binder.
Inventors: |
Saito; Shinji (Odawara-shi,
Kanagawa, JP), Araki; Hiroaki (Odawara-shi, Kanagawa,
JP), Ejiri; Kiyomi (Odawara-shi, Kanagawa,
JP), Ogawa; Hiroshi (Odawara-shi, Kanagawa,
JP), Mizuno; Chiaki (Odawara-shi, Kanagawa,
JP) |
Family
ID: |
17184528 |
Appl.
No.: |
07/110,317 |
Filed: |
October 20, 1987 |
Foreign Application Priority Data
|
|
|
|
|
Oct 20, 1986 [JP] |
|
|
61-248862 |
|
Current U.S.
Class: |
428/844.6;
427/128; 428/323; 428/413; 428/900; G9B/5.247 |
Current CPC
Class: |
G11B
5/7023 (20130101); Y10S 428/90 (20130101); Y10T
428/31511 (20150401); Y10T 428/25 (20150115) |
Current International
Class: |
G11B
5/702 (20060101); G11B 005/70 () |
Field of
Search: |
;428/522,694,900,328,329,695,413,418 ;252/62.54 ;427/128,131
;360/134-136 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Thibodeau; Paul J.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak and
Seas
Claims
We claim:
1. A magnetic recording medium comprising a non-magnetic support
and a magnetic recording layer provided on the support which
comprises a binder and a ferromagnetic powder dispersed therein,
wherein said binder contains a resin component having an epoxy
group in the range of 1.times.10.sup.-4 to 1.times.10.sup.-2 mols/g
of said resin component, said resin component being selected from
the group consisting of a vinyl chloride copolymer, a vinylidene
chloride copolymer, a polyester resin, an acrylic resin, a
polyvinyl acetal resin, a polyvinyl butyral resin, a phenoxy resin,
a butadieneacrylonitile copolymer, and a polyurethane resin, and
said ferromagnetic powder contains water in an amount corresponding
to moles of 1-5 times as much as the number of moles of the epoxy
group contained in the binder.
2. The magnetic recording medium as claimed in claim 1, wherein
said ferromagnetic powder contains water in an amount corresponding
to moles of 2-4 times as much as the number of moles of the epoxy
group contained in the binder.
3. The magnetic recording medium as claimed in claim 1, wherein
said ferromagnetic powder is a ferromagnetic metal powder.
4. The magnetic recording medium as claimed in claim 1, wherein
said resin component having an epoxy group is a vinyl chloride
copolymer having an epoxy group.
5. The magnetic recording medium as claimed in claim 1, wherein
said resin component having an epoxy group is contained in the
magnetic recording layer in an amount of 5 to 50 parts by weight
based on 100 parts by weight of the ferromagnetic powder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium
comprising a nonmagnetic support and a magnetic recording
layer.
2. Description of Prior Art
A magnetic recording medium has been widely used as a tape for
recording music (i.e., an audio tape), a video tape and a floppy
disc. The magnetic recording medium basically comprises a
nonmagnetic support and a magnetic recording layer provided on the
support, and the magnetic recording layer comprises a binder and a
ferromagnetic powder dispersed therein.
The magnetic recording medium is desired to show high levels in
various properties such as electromagnetic conversion
characteristics, running endurance and running property.
Particularly, the recording medium is desired to show excellent
electromagnetic conversion characteristics. For example, an audio
tape is required to have high reproducibility of original sounds,
and a video tape is required to have high reproducibility of an
original image. Such high electromagnetic conversion
characteristics is desired particularly in the case of using an 8
mm type video tape recorder.
It is known that the electromagnetic conversion characteristics of
the magnetic recording medium using a ferromagnetic powder greatly
varies depending upon dispersibility (or dispersed condition) of
the ferromagnetic powder in the magnetic recording layer. In more
detail, even if a ferromagnetic powder having excellent magnetic
property is used for the purpose of enhancing the electromagnetic
conversion characteristics of the resulting medium, the excellent
magnetic property of the ferromagnetic powder is not reflected on
the enhancement of the electromagnetic conversion characteristics
when the ferromagnetic powder is poorly dispersed in the recording
layer.
For improving the dispersibility of the ferromagnetic powder in the
magnetic recording layer, there has been utilized a method of
kneading or dispersing the ferromagnetic powder for a long period
of time in the preparation of a magnetic paint for forming a
magnetic recording layer. However, such longtime kneading or
dispersing causes deterioration of the magnetic property of the
ferromagnetic powder, and therefore a measure of incorporating a
polar group into a resin component for forming a binder of a
recording layer is recently utilized so as to make the binder show
a favorable affinity for the ferromagnetic powder.
For example, Japanese Patent Provisional Publication No.
59(1984)-5424 discloses a magnetic recording medium in which a
resin component having a specific polar group such as a sulfonic
acid metal salt group is employed in an amount of not less than 50
wt.% as a binder of the magnetic recording layer using a
ferromagnetic metal powder of needle shape having a coercive force
(Hc) of not less than 1000 Oe and a specific surface area (S-BET)
of not less than 45 m.sup.2 /g (determined according to a BET
method). By employing such resin having a specific polar group as a
resin component of the binder, a magnetic recording medium in which
the ferromagnetic powder is well dispersed in the magnetic
recording layer can be prepared, and the resulting medium is highly
improved in the electromagnetic conversion characteristics.
SUMMARY OF THE INVENTION
The present inventors have studied to further improve the
dispersibility of a ferromagnetic powder so as to further enhance
the electromagnetic conversion characteristics of the recording
medium.
It is an object of the present invention to provide a magnetic
recording medium such as an audio tape or a video tape which is
improved in electromagnetic conversion characteristics.
There is provided by the present invention a magnetic recording
medium comprising a nonmagnetic support and a magnetic recording
layer provided on the support which comprises a binder and a
ferromagnetic powder dispersed therein, wherein said binder
contains a resin component having an epoxy group and said
ferromagnetic powder contains water in an amount corresponding to
moles of 1-5 times (preferably 2-4 times) as much as the number of
moles of the epoxy group contained in the binder.
In the present invention, a resin containing a resin component
having an epoxy group is employed as a binder for the formation of
a magnetic recording layer, and a specific amount of water is
incorporated into the ferromagnetic powder (most of the water
contained in the ferromagnetic powder is thought to be in the
adsorbed state on the surface of the powder), whereby the
dispersibility of the ferromagnetic powder in the recording layer
is highly improved, and as a result, the resulting magnetic
recording medium is prominently enhanced in the electromagnetic
conversion characteristics.
In the case of using a ferromagnetic metal powder, the
ferromagnetic metal powder is apt to be poorly dispersed in the
binder for the reasons of of its surface property and fine
particles thereof, and accordingly the present invention is
particularly advantageously applied to a magnetic recording medium
such as an audio tape or an 8 mm type video tape using a
ferromagnetic metal powder.
DETAILED DESCRIPTION OF THE INVENTION
The magnetic recording medium of the present invention basically
comprises a nonmagnetic support and a magnetic recording layer
provided on the support which comprises a ferromagnetic powder
dispersed in a binder.
As a material of the nonmagnetic support, there can be selected
from those conventionally used for a nonmagnetic support of a known
magnetic recording medium. Examples of the material include
polyethylene terephthalate, polypropylene, polycarbonate,
polyethylene naphthalate, polyamide, polyamideimide, polyimide, and
metallic foils such as aluminum foil and stainless steel foil. The
thickness of the nonmagnetic support is generally in the range of 3
to 50 .mu.m, preferably in the range of 5 to 30 .mu.m.
The nonmagnetic support may have a back layer (or backing layer) on
the opposite side of the side where a magnetic recording layer is
to be coated.
There is no specific limitation on the ferromagnetic powder
employable in the invention, and various ferromagnetic powders such
as powders of .gamma.-iron oxide and Co-containing .gamma.-iron
oxide can be employed. Preferred is a ferromagnetic metal powder.
The ferromagnetic metal powder is a powder mainly containing a
ferromagnetic metal such as iron, cobalt, nickel and alloy
thereof.
As a typical ferromagnetic metal powder, there can be mentioned a
ferromagnetic alloy powder containing a metal component of at least
75 wt.% in which at least 80 wt.% of the metal component comprises
at least one ferromagnetic metal or metal alloy (e.g., Fe, Co, Ni,
Fe-Co, Fe-Ni, Co-Ni and Co-Ni-Fe) and the remaining metal
component, if present, comprises other atom(s) (e.g., Si, S, Sc,
Ti, V, Cr, Mn, Cu, Zn, Y, Mo, Rh, Pd, Ag, W, Sn, Sb, B, Te, Ba, Ta,
Re, P, Au, Hg, Bi, La, Ce, Pr, Nd, Pb, Zn). The ferromagnetic metal
powder may contain a small amount hydroxide or oxide.
The ferromagnetic metal powder preferably has a specific surface
area of not less than 42 m.sup.2 /g, more preferably not less than
45 m.sup.2 /g, and a coercive force of not less than 800 Oe, more
preferably not less than 1,000 Oe. The ferromagnetic metal powder
normally used is in a needle shape, grain shape, dice shape, rice
shape or plate shape. Preferred is a ferromagnetic metal powder in
a needle shape. In the magnetic recording medium of the invention,
even if the above-mentioned ferromagnetic metal powder of needle
shape having a high coercive force is used, the ferromagnetic metal
powder is well dispersed in the recording layer by introducing a
specific amount of water into the ferromagnetic powder and using a
resin component having an epoxy group as a binder component,
whereby the excellent magnetic property of the ferromagnetic metal
powder hardly deteriorates.
Adjustment of the amount of water introduced into the ferromagnetic
powder to be incorporated into the magnetic recording layer of the
recording medium according to the invention is easily made by
storing the ferromagnetic powder in a container which is adjusted
with respect to humidity.
The magnetic recording layer preferably contains an abrasive.
Normally used is an abrasive having a mean particle diameter of 0.1
to 1.0 .mu.m, preferably 0.1 to 0.5 .mu.m. The amount of the
abrasive contained in the magnetic recording layer is generally in
the range of 1 to 10 parts by weight, preferably 2 to 8 parts by
weight, more preferably 3 to 6 parts by weight, based on 100 parts
by weight of the ferromagnetic powder. Examples of the abrasives
include .alpha.-alumina, chromium oxide, .alpha.-iron oxide.
The magnetic recording layer of the magnetic recording medium
according to the invention contains a binder component (resin
component) having an epoxy group in an amount of preferably 5 to 50
parts by weight, more preferably 10 to 30 parts by weight, based on
100 parts by weight of the ferromagnetic powder.
Examples of the resin components composing a base component of the
binder having an epoxy group include vinyl chloride copolymers,
vinylidene chloride copolymers, polyester resins, acrylic resins,
polyvinyl acetal resins, polyvinyl butyral resins, phenoxy resins,
epoxy resins, butadiene/acrylonitrile copolymers, polyurethane
resins and urethane epoxy resins. These resins can be employed in
the invention independently or in combination. Particularly
preferred is a vinyl chloride copolymer.
In the invention, it is preferred to use a combination of a vinyl
chloride copolymer having an epoxy group and a polyurethane resin
as a resin component of the binder.
The amount of the epoxy group contained in the resin component
having an epoxy group is preferably in the range of
1.times.10.sup.-4 to 1.times.10.sup.-2 mol/g.
The number average molecular weight of the vinyl chloride copolymer
is generally in the range of 10,000 to 200,000, preferably 10,000
to 100,000, more preferably 15,000 to 60,000.
The vinyl chloride copolymer having an epoxy group can be prepared
by copolymerizing a vinyl chloride monomer and a monomer having an
epoxy group such as glycidyl (meth)acrylate according to a known
method. If desired, the vinyl chloride monomer can also be
copolymerized with a monomer having other polar groups than the
epoxy group such as 2-(meth)acrylamido-2-methylpropane sulfonic
acid, vinyl sulfonic acid, alkali metal salt thereof, (meth)acrylic
acid-2-ethyl sulfonate, alkali metal salt thereof, maleic anhydride
and (meth)acrylic acid, and (meth)acrylic acid-2-phosphoric acid
ester.
In the preparation of a vinyl chloride copolymer, other monomers
such as vinyl ether, .alpha.-monoolefin, acrylic acid ester,
unsaturated nitrile, aromatic vinyl and vinyl ester can be
incorporated in combination provided that the incorporation thereof
does not give an adverse effect to the resulting vinyl chloride
copolymer.
In the case of using the vinyl chloride copolymer in combination
with the polyurethane resin as a binder, the ratio between the
vinyl chloride copolymer and the polyurethane resin is generally in
the range of 35:65 to 99:1 (vinyl chloride copolymer:polyurethane
resin, by weight), preferably 40:60 to 96:4. In the case of using
such combination, the ferromagnetic powder is apt to be better
dispersed as compared with the case of using other resin
component.
Further, the binder is preferably a curable material in which a
polyisocyanate compound is added to the above-mentioned vinyl
chloride copolymer and polyurethane resin.
As the polyisocyanate compound, there can be mentioned those
conventionally employed. Examples of the polyisocyanate compound
employable in the invention include reaction products of 3 moles of
diisocyanate (e.g., diphenylmethane-4,4'-diisocyanate and tolylene
diisocyanate) and 1 mol of trimethylolpropane, burette adducts of 3
moles of hexamethylene diisocyanate, isocyanurate adduct compounds
of 5 moles of tlyledine isocyanate, isocyanurate adduct compounds
of 3 moles of tolylene diisocyanate and 2 moles of hexamethylene
diisocyanate, and polymers of diphenylmethane diisocyanate.
The amount of the polyisocyanate compound is generally the same or
not larger than that of the employed polyurethane resin.
By using the above-mentioned polyurethane resin, vinyl chloride
copolymer and polyisocyanate compound as the binder, the
polyisocyanate compound can make a three dimensional crosslinking
structure between the polyurethane resin and the vinyl chloride
copolymer, and thereby a binder of high strength can be
prepared.
The magnetic recording layer according to the invention may further
contain other additives such as a lubricant and an antistatic
agent.
A process of the magnetic recording medium of the present invention
is described hereinafter.
In the first place, the above-described ferromagnetic powder having
a water content specified in the invention, binder and other
additives (if desired) are dispersed in an organic solvent to
prepare a magnetic paint. The magnetic paint is then coated over a
nonmagnetic support to give a coated layer of the magnetic paint
having dry thickness of 0.2 to 10 .mu.m. The support with the
coated layer is then subjected to various treatments such as a
magnetic orientation, a drying process, a surface smoothening
process and a curing treatment. The resulting sheet is then cut or
slit into a desired shape to prepare a magnetic recording
medium.
The magnetic recording layer is generally provided on the
nonmagnetic support by directly coating a magnetic paint over the
support, but it is also possible to provide the recording layer on
the support by way of an adhesive layer or an undercoating
layer.
Processes for the preparation of a magnetic paint, a coating method
and various treatments such as a magnetic orientation, a drying
process, a surface smoothening process and a curing treatment are
already known, and those known processes can be applied to the
magnetic recording medium of the invention.
The examples and the comparison examples of the present invention
are given below. In the following examples, the expression
"part(s)" means "part(s) by weight", unless otherwise
specified.
EXAMPLE 1
______________________________________ Composition of Magnetic
Paint ______________________________________ Ferromagnetic metal
powder 100 parts Vinyl chloride copolymer containing 20 parts epoxy
group Polyester polyurethane resin 5 parts .alpha.-alumina 3 parts
Carbon black 1 part Lauric acid 3 parts Butyl acetate 350 parts
______________________________________
The ferromagnetic metal powder listed above is a Fe-Zn-Ni alloy
having a copolymerization ratio of 94:4:2 (Fe:Zn:Ni), a specific
surface area (S-BET) of 40 m.sup.2 /g, a coercive force (Hc) of
1,200 Oe, a saturation magnetic moment (.sigma.s) of 135 emu/g, and
a water content of 4.0.times.10.sup.-4 mol/g. The vinyl chloride
copolymer containing epoxy group also listed above is a vinyl
chloride copolymer having an epoxy content of 8.4.times.10.sup.-4
mol/g and a polymerization degree of 300, in which vinyl chloride,
2-acrylamido-2-methylpropane sodium sulfonate and glycidyl
methacrylate are copolymerized.
The components indicated above were kneaded in a sand mill to
prepare a magnetic paint. The magneti paint was coated over a
surface of a polyethylene terephthalate support of 7 .mu.m thick by
means of a reverse roll to give a coated layer of the magnetic
paint having thickness of 4.0 .mu.m (in dry basis).
The nonmagnetic support with the coated layer of the magnetic paint
was then subjected to a magnetic orientation under wet condition,
and subsequently subjected to a drying process and a
supercalendering. The resulting sheet was slit to give an audio
tape having a width of 3.8 mm.
EXAMPLE 2
The procedure of Example 1 was repeated except for varying the
water content in the ferromagnetic metal powder to
2.0.times.10.sup.-4 mol/g to prepare an audio tape.
EXAMPLE 3
The procedure of Example 1 was repeated except for varying the
water content in the ferromagnetic metal powder to
7.0.times.10.sup.-4 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 1
The procedure of Example 1 was repeated except for using a vinyl
chloride copolymer not containing any epoxy group (vinyl
chloride/vinyl acetate/maleic anhydride copolymer) instead of the
vinyl chloride copolymer containing an epoxy group to prepare an
audio tape.
COMPARISON EXAMPLE 2
The procedure of Example 1 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.0.times.10.sup.-4 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 3
The procedure of Example 1 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.0.times.10.sup.-3 mol/g to prepare an audio tape.
The audio tapes obtained in Examples 1 to 3 and Comparison Examples
1 to 3 were evaluated on surface glossiness of the magnetic
recording layer, squareness ratio, maximum output level (MOL),
saturation output level (SOL) and occurrence of stain on a tape pad
and a magnetic head equipped in the recording apparatus (tape
recorder) according to the following tests.
The results of the evaluations are set forth in Table 1.
Surface glossiness
The surface glossiness of the magnetic layer was measured by using
a surface glossmeter (GK-45D type, produced by Suga Testing Machine
Co., Ltd.). The surface glossiness of a standard black surface is
87% when measured by the same glossmeter.
Squareness ratio
The squareness ratio was determined by measuring a ratio of Br/Bm
at an external magnetic field intensity (Hm) of 2 KOe (159 KA/m) by
means of a vibrating sample magnetic flux measuring machine
(produced by Toei Industry Co., Ltd.).
Maximum output level (MOL)
A signal of 315 Hz was recorded on the audio tape, and the recorded
signal was reproduced to measure its maximum output level (MOL,
third high frequency: 3%) by means of a measuring machine
(TCK-777ESII type, produced by Sony Corp., Ltd.). The maximum
output level is expressed by a relative value based on the MOL
value of the audio tape obtained in Comparison Example 1 being 0
dB.
Saturation output level (SOL)
A signal of 10 kHz was recorded on the audio tape, and the recorded
signal was reproduced to measure its saturation output level (SOL)
by means of the same measuring machine as that used for measuring
the above-mentioned MOL values. The saturation output level is
expressed by a relative value based on the SOL value of the audio
tape obtained in Comparison Example 1 being 0 dB.
Occurrence of stain
The audio tape was repeatedly run in a commercially available tape
recorder at 20 times, and then occurrence of stain on a tape pad
and a magnetic head equipped in the tape recorder was observed.
TABLE 1 ______________________________________ Example Com. Example
1 2 3 1 2 3 ______________________________________ Water/Epoxy 2.4
1.4 4.2 -- 0.6 6.0 (molar ratio) Surface 251 247 250 220 227 233
glossiness (%) Squareness 0.86 0.85 0.85 0.78 0.82 0.81 ratio MOL
(dB) +1.8 +1.4 +1.4 0 +0.6 +0.3 SOL (dB) +0.6 +0.5 +0.6 0 +0.1 +0.2
Occurrence none none none ob- none none of stain served
______________________________________
EXAMPLE 4
The procedure of Example 1 was repeated except for using a vinyl
chloride copolymer having an epoxy content of 3.2.times.10.sup.-4
mol/g and the same other conditions as those of the vinyl chloride
copolymer used in Example 1, and varying the water content in the
ferromagnetic metal powder to 1.5.times.10.sup.-4 mol/g, to prepare
an audio tape.
EXAMPLE 5
The procedure of Example 4 was repeated except for varying the
water content in the ferromagnetic metal powder to
8.0.times.10.sup.-5 mol/g to prepare an audio tape.
EXAMPLE 6
The procedure of Example 4 was repeated except for varying the
water content in the ferromagnetic metal powder to
3.0.times.10.sup.-4 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 4
The procedure of Example 4 was repeated except for varying the
water content in the ferromagnetic metal powder to
5.5.times.10.sup.-5 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 5
The procedure of Example 4 was repeated except for varying the
water content in the ferromagnetic metal powder to
4.0.times.10.sup.-4 mol/g to prepare an audio tape.
The audio tapes obtained in Examples 4 to 6 and Comparison Examples
4 and 5 were evaluated on surface glossiness of the magnetic
recording layer, squareness ratio, maximum output level (MOL),
saturation output level (SOL) and occurrence of stain on a tape pad
and a magnetic head equipped in the recording apparatus (tape
recorder) according to the aforementioned tests.
The results of the evaluations are set forth in Table 2.
TABLE 2 ______________________________________ Example Com. Example
4 5 6 4 5 ______________________________________ Water/Epoxy 2.3
1.3 4.7 0.9 6.3 (molar ratio) Surface 248 245 247 224 228
glossiness (%) Squareness 0.85 0.84 0.84 0.81 0.80 ratio MOL (dB)
+1.5 +1.2 +1.2 +0.3 +0.1 SOL (dB) +0.5 +0.5 +0.5 +0.1 +0.1
Occurrence none none none observed observed of stain
______________________________________
EXAMPLE 7
The procedure of Example 1 was repeated except for using a vinyl
chloride copolymer having an epoxy content of 1.2.times.10.sup.-3
mol/g and the same other conditions as those of the vinyl chloride
copolymer used in Example 1, and varying the water content in the
ferromagnetic metal powder to 6.0.times.10.sup.-4 mol/g, to prepare
an audio tape.
EXAMPLE 8
The procedure of Example 7 was repeated except for varying the
water content in the ferromagnetic metal powder to
3.0.times.10.sup.-4 mol/g to prepare an audio tape.
EXAMPLE 9
The procedure of Example 7 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.0.times.10.sup.-3 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 6
The procedure of Example 7 was repeated except for varying the
water content in the ferromagnetic metal powder to
2.0.times.10.sup.-4 mol/g to prepare an audio tape.
COMPARISON EXAMPLE 7
The procedure of Example 7 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.6.times.10.sup.-3 mol/g to prepare an audio tape.
The audio tapes obtained in Examples 7 to 9 and Comparison Examples
6 and 7 were evaluated on surface glossiness of the magnetic
recording layer, squareness ratio, maximum output level (MOL),
saturation output level (SOL) and occurrence of stain on a tape pad
and a magnetic head equipped in the recording apparatus (tape
recorder) according to the aforementioned tests.
The results of the evaluations are set forth in Table 3.
TABLE 3 ______________________________________ Example Com. Example
7 8 9 6 7 ______________________________________ Water/Epoxy 2.5
1.3 4.2 0.8 6.3 (molar ratio) Surface 255 251 253 232 237
glossiness (%) Squareness 0.86 0.86 0.85 0.82 0.80 ratio MOL (dB)
+1.9 +1.8 +1.6 +0.6 +0.2 SOL (dB) +0.8 +0.6 +0.7 +0.2 +0.3
Occurrence none none none none none of stain
______________________________________
EXAMPLE 10
______________________________________ Composition of Magnetic
Paint ______________________________________ Ferromagnetic metal
powder 100 parts Vinyl chloride copolymer containing 12 parts epoxy
group Polyester polyurethane resin 8 parts .alpha.-alumina 5 parts
Stearic acid 2 parts Butyl stearate 2 parts Cyclohexanone 100 parts
Methyl ethyl ketone 250 parts
______________________________________
The ferromagnetic metal powder listed above is a Fe-Zn-Ni alloy
having a copolymerization ratio of 94:4:2 (Fe:Zn:Ni), a specific
surface area (S-BET) of 50 m.sup.2 /g, a coercive force (Hc) of
1,400 Oe, a saturation magnetic moment (.sigma.s) of 125 emu/g, and
a water content of 2.4.times.10.sup.-4 mol/g. The vinyl chloride
copolymer containing epoxy group also listed above is a vinyl
chloride copolymer having an epoxy content of 8.4.times.10.sup.-4
mol/g and a polymerization degree of 300, in which vinyl chloride,
2-acrylamido-2-methylpropane sodium sulfonate and glycidyl
methacrylate are copolymerized.
The components indicated above were kneaded in a sand mill to give
a dispersion. To the dispersion was added 5 parts of a
polyisocyanate compound, and they were kneaded to prepare a
magnetic paint. The magnetic paint was coated over a surface of a
polyethylene terephthalate support of 10 .mu.m thick by means of a
reverse roll to give a coated layer of the magnetic paint having
thickness of 3.0 .mu.m (in dry basis). The nonmagnetic support with
the coated layer of the magnetic paint was then subjected to a
magnetic orientation under wet condition, and subsequently
subjected to a drying process and a supercalendering. The resulting
sheet was slit to give a video tape having a width of 8 mm.
EXAMPLE 11
The procedure of Example 10 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.2.times.10.sup.-4 mol/g to prepare a video tape.
EXAMPLE 12
The procedure of Example 10 was repeated except for varying the
water content in the ferromagnetic metal powder to
4.2.times.10.sup.-4 mol/g to prepare a video tape.
COMPARISON EXAMPLE 8
The procedure of Example 10 was repeated except for using a vinyl
chloride copolymer not containing any epoxy group (vinyl
chloride/vinyl acetate/maleic anhydride copolymer) instead of the
vinyl chloride copolymer containing an epoxy group to prepare a
video tape.
COMPARISON EXAMPLE 9
The procedure of Example 10 was repeated except for varying the
water content in the ferromagnetic metal powder to
6.0.times.10.sup.-5 mol/g to prepare a video tape.
COMPARISON EXAMPLE 10
The procedure of Example 10 was repeated except for varying the
water content in the ferromagnetic metal powder to
6.0.times.10.sup.-4 mol/g to prepare a video tape.
The video tapes obtained in Examples 10 to 12 and Comparison
Examples 8 to 10 were evaluated on surface glossiness of the
magnetic recording layer and squareness ratio according to the
aforementioned tests, and further evaluated on video output level,
S/N ratio and tendency of clogging on a magnetic head according to
the following tests.
The results of the evaluations are set forth in Table 4.
Video output level (VS)
A signal of 4 MHz was recorded on the video tape, and the recorded
signal was reproduced to measure a video output level by means of a
measuring machine (FUJIX-8, produced by Fuji Photo Film Co., Ltd.).
The video output is expressed by a relative value based on the
video output of the video tape obtained in Comparison Example 8
being 0 dB.
S/N ratio
A signal of 4 MHz was recorded on the video tape, and the recorded
signal was reproduced to measure a S/N ratio by means of a
measuring machine (FUJIX-8, produced by Fuji Photo Film Co., Ltd.).
The S/N ratio is expressed by a relative value based on the S/N
ratio of the video tape obtained in Comparison Example 8 being 0
dB.
Clogging on a magnetic head
The video tape was repeatedly run in a commercially available tape
recorder (FUJIX-8, produced by Fuji Photo Film Co., Ltd.) at 20
times, and then the tendency of clogging on a magnetic head was
observed.
TABLE 4 ______________________________________ Example Com. Example
10 11 12 8 9 10 ______________________________________ Water/Epoxy
2.4 1.2 4.2 -- 0.6 6.0 (molar ratio) Surface 259 254 257 225 230
240 glossiness (%) Squareness 0.83 0.82 0.82 0.76 0.81 0.78 ratio
S/N ratio +1.0 +0.8 +0.9 0 +0.2 +0.2 (dB) Video output +1.2 +1.0
+1.0 0 +0.3 +0.3 (dB) Clogging on none none none ob- none none
magnetic head served ______________________________________
EXAMPLE 13
The procedure of Example 10 was repeated except for using a vinyl
chloride copolymer having an epoxy content of 3.2.times.10.sup.-4
mol/g and the same other conditions as those of the vinyl chloride
copolymer used in Example 10, and varying the water content in the
ferromagnetic metal powder to 9.0.times.10.sup.-5 mol/g, to prepare
a video tape.
EXAMPLE 14
The procedure of Example 13 was repeated except for varying the
water content in the ferromagnetic metal powder to
4.8.times.10.sup.-5 mol/g to prepare a video tape.
EXAMPLE 15
The procedure of Example 13 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.8.times.10.sup.-4 mol/g to prepare a video tape.
COMPARISON EXAMPLE 11
The procedure of Example 13 was repeated except for varying the
water content in the ferromagnetic metal powder to
3.3.times.10.sup.-5 mol/g to prepare a video tape.
COMPARISON EXAMPLE 12
The procedure of Example 13 was repeated except for varying the
water content in the ferromagnetic metal powder to
2.4.times.10.sup.-4 mol/g to prepare a video tape.
The video tapes obtained in Examples 13 to 15 and Comparison
Examples 11 and 12 were evaluated on surface glossiness of the
magnetic recording layer, squareness ratio, video output level, S/N
ratio and tendency of clogging on a magnetic head according to the
aforementioned tests.
The results of the evaluations are set forth in Table 5.
TABLE 5 ______________________________________ Example Com. Example
13 14 15 11 12 ______________________________________ Water/Epoxy
2.3 1.3 4.7 0.9 6.3 (molar ratio) Surface 256 252 254 222 236
glossiness (%) Squareness 0.82 0.82 0.81 0.80 0.77 ratio S/N ratio
(dB) +1.0 +0.7 +0.7 +0.1 +0.1 Video output (dB) +1.1 +0.9 +0.8 +0.0
+0.2 Clogging on none none none observed observed magnetic head
______________________________________
EXAMPLE 16
The procedure of Example 10 was repeated except for using a vinyl
chloride copolymer having an epoxy content of 1.2.times.10.sup.-4
mol/g and the same other conditions as those of the vinyl chloride
copolymer used in Example 10, and varying the water content in the
ferromagnetic metal powder to 3.6.times.10.sup.-4 mol/g, to prepare
a video tape.
EXAMPLE 17
The procedure of Example 16 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.8.times.10.sup.-4 mol/g to prepare a video tape.
EXAMPLE 18
The procedure of Example 16 was repeated except for varying the
water content in the ferromagnetic metal powder to
6.0.times.10.sup.-4 mol/g to prepare a video tape.
COMPARISON EXAMPLE 13
The procedure of Example 16 was repeated except for varying the
water content in the ferromagnetic metal powder to
1.2.times.10.sup.-4 mol/g to prepare a video tape.
COMPARISON EXAMPLE 14
The procedure of Example 16 was repeated except for varying the
water content in the ferromagnetic metal powder to
9.0.times.10.sup.-4 mol/g to prepare a video tape.
The video tapes obtained in Examples 16 to 18 and Comparison
Examples 13 and 14 were evaluated on surface glossiness of the
magnetic recording layer, squareness ratio, video output level, S/N
ratio and tendency of clogging on a magnetic head according to the
aforementioned tests.
The results of the evaluations are set forth in Table 6.
TABLE 6 ______________________________________ Example Com. Example
16 17 18 13 14 ______________________________________ Water/Epoxy
2.5 1.3 4.2 0.8 6.3 (molar ratio) Surface 264 258 260 245 248
glossiness (%) Squareness 0.83 0.83 0.82 0.81 0.78 ratio S/N ratio
(dB) +1.2 +1.1 +1.1 +0.3 +0.4 Video output (dB) +1.4 +1.2 +1.2 +0.5
+0.4 Clogging on none none none none none magnetic head
______________________________________
* * * * *